1. Field of the Invention
The invention relates to a method and a system for monitoring the functional capability of a particle detector, using a particle filter connected upstream, in the flow direction, of the particle detector. The invention also relates to a computer program (computer program product) suitable for use in such a system.
2. Prior Art
The concentration of particles, in particular soot particles, in diesel internal combustion engines is often measured by electrical methods. From German Patent Disclosure DE 198 53 584 A1, for instance, a sensor for detecting soot particles is known which includes a first high-voltage electrode and a second ground electrode. In operation, there is a flow of exhaust gas through the space between the electrodes, and either the electrical voltage beyond which sparks occur between the two electrodes, or, if the electrical voltage is kept constant, the magnitude of the ionization current flowing between the two electrodes is used as a standard for the concentration of soot particles in the exhaust gas. Other possibilities are charging the particles by means of an ionization source, such as a corona discharge, or by the combustion process itself. The charged particles are then passed through a suitable detector structure (grid) and can give up their charge again there. The measured current is thus a measure for the charge picked up by the particles, and for a known degree of ionization of the particles, it is also a standard for the number of particles that reach the detector.
Particles that have been charged by one of the methods described above or that become charged on their own from a combustion process can also cause a shift in the charge in a detector structure by influence, which can in turn be proved detected. The known detection methods thus use the measurement of small currents or charge shifts.
For various reasons (to meet legal requirements, and for reasons of safety and environmental aspects), there is a need for the detection devices described above to be monitored for proper functioning. This is true particularly since the charges or charge shifts to be detected are very small, and interference can incorrectly lead to a finding of proper operation.